Electron discharge device for very high frequencies



Dec. 29, 1942. n Q H, BLACK 2,306,860

ELECTRON DISCHARGE DHVIICE FOR VERY HIGH FREQUENGIES Filed Aug. 29, 1940l lll/l l/ /nyenor f I Atta/'ne Patented Dee. 29,'V 1942 ELECTRONDISCHARGE DEVICE FOR VERY HIGHFREQUENCIESy Donald Harrison Black,London, England, assignor to International Standard Electric Corpora'-tion, New York, N. Y

Application August 29, 1940, Serial No. 354,657

In Great 3 Claims.

This invention relates to electron discharge de-v vices Aof theso-called velocity modulated type.

Briefly the operation of such devices is as follows:

A beam of .electrons of uniform velocity is passed through a gap in aresonator to which is applied the resonant frequency, across the gap,the electrons are accelerated or decelerated according to the phase ofthe oscillations at the time at which they pass.r After In passingleaving this resonant system,`or modulator, the

electrons pass through a eld-free space, and while in this space acertain degree of bunching of the electrons takes place. This is due toaccelerated electrons catching up on the slower ones which preceded themthrough the modulating gap. The bunched electrons then pass through asecond resonant system which is in oscillation and the circuit is soarranged that, owing to this bunching, more electrons will bedecelerated on passing through the gap than will be accelerated. If sucha state of affairs exists, then the energy given up to the secondresonant system by the electrons which are decelerated will exceed theenergy extracted from it by those which are accelerated, the net resultbeing a gain in energy by the resonant system.

In the known systems, a single beam of electrons is passed throughresonators of various types and some difilculty is experienced inobtaining beams of the required magnitude. In the suggestions so far putforward the source of electrons is usually external to the resonators.In the arrangements now proposed, the electron source is partly orcompletely enclosed by the resonators and some ofthe diliicultiesencountered in the formation of beams are largely overcome.

In one aspect the invention resides in an electron discharge device ofthe velocity modulated type comprising two co-axial cavity resonators ofannular cross-section lying one within the other and an electrode systemfor projecting electrons radially through grids or apertures in theresonator walls.

In another aspect the invention resides in an y electron dischargedevice of the velocity modulated type wherein two resonant cavities ofannular cross-section are deiined by co-axial cylindrical surfaces, anelectron source being provided along the axis of the structure forprojecting electrons radially through grids or apertures in thecylindrical surfaces. y

These and other further aspects of novelty and invention willhereinafter be pointed out or will become apparent from a reading of thefollow- Britain September 13, 1939 (Cl. Z50-27.5)

ing specification in conjunction with the drawing included herewith. Insaid drawing Fig. 1 is a cross-sectional elevation of an electrondischarge' device Aincorr'noiating features of the invention;

Fig. z is a cross-sectional view taken substantially in the kplane of2-2 in Fig. l; and

Figs. 3 and 4 are further cross-sectional views taken transversely tothe plane of Fig. 1,

Referring to Fig. 1, which is a section through the structure a cathodeI is surrounded by av series of concentric grids 2, 3, 5, 1` 9, the axisof revolution being X-`X. The grids are represented by dottedlines butinpractice would probably be of squirrel cage formation, up from a seriesof rods. Fig.'2 shows a sectional view across the line 2-2 of Fig. 1. Itwill be noticed that the rods forming the respective grids lie on radiallines extending from the cathode. This is a preferred arrangement inorder to reduce the number lof electrons collected by the grids.

Grid 2 is normally operated at a negative potential with respect to thecathode and its purposeis to control the magnitude of the spacecurrent.k Grids 3 and 5 lormrportions oi cylinders and 6 respectively.The spaces between the ends of the cylinders are closed by the annulardiscs I6 and I9. The two cylinders with their end discs thus form aresonator of the concentric line type. Similarly grids 1 and 9 formportions of the cylinders 8 and I which with the end discs I1 and I8form a second concentric line resonator. Cylinders 6 and 8 are Joined bytwo discs placed at the ends of the grid portions as shown. The cylinderI I collects the electrons which pass through the system. A

The electrons in passing from the cathode I to the collector II passthrough two resonators. If the inner resonator has oscillations appliedto it, the electrons will be velocity modulated as described above.While moving between the field free space between the inner and theouter cylinders, bunching or the electrons will take place and energywill be imparted to the outer resonator. Oscillations set up in thesecond resonator may be taken ol by means of lead I2 which contacts withthe cylinder 8 through a concentric tube I3. Other methods forwithdrawing energy from the second resonator are possible.

If the device is to be used as an oscillator, then some of the energyfrom the outer resonator must be fed back to the inner resonator. Onemethod of carrying this out is shown in Fig. 1 and in Fig. 3 which is asection across the line being made Y 3-3 Fig. 1. An elongated loop ofwire Il has 'one limb, in fthe centre of a connecting tube I 5 andtheother'limb just outside@ in the wall o! Il. The rounded ends of the'99p project into the inner and outer resonators.v v`'*Ihe couplingbetween the two resonators displacement of the loop which exposes agreater area of loop in one resonator than in the other.

The permissible-distance between grids!! andy-5 and between grids, 1,'and, 9 speed of the electrons and the frequency of operation. 'I'he timeof ilight across these gaps n'iust4 is varied by a lateral dependsk uponthe v not exceed a certain fraction of thel period Iof kone A completeoscillation. In some 'cases it ymay be',

found that the grids must be placed closertogether than isdesirable forkthespacing Vbetween the cylinders if these are to form anfefiicient'vresonator. Fig. 4 shows how this may Abe imf byannular discs, said innerand said outer pairs" being coaxial with each spaced annular discsbetween said inner and outer pairs of cylinders providing asubstantially ileldother, a pair of axially :I vfree ,drift/space.,generally longitudinally extendproved by replacing the rods with stripslofmetal set radially. The could then be placed on the inner cumferencesof 1 and 9 respectively. i Y i Foreillcientoperation of such adevicethetwo resonators must be exactlyl in tune, nator may have a xedfrequency vand the other may beA tuned by sliding the end -disclsof theinner resonator up and down.

Various methods are available for ensuring that the electron paths arein vacuumifor'example the structure may be wholly enclosedor'parts ofthe resonators may'form parts of envelope.

an'evacua'ted .What is claimed is: t l

walls of the cylinders' and i0; and outer ciri One reso# `1. An electronldischarge device including an inner pair of coaxialvsheet-metalcylinders joined at their ends by annular discs, an outer pair `ofcoaxial sheet-metal cylinders joined at their ends by annular discs.said inner and said outer pairs said cylinders, through said tube intothe two cylinders. a' 3. An- .e1ectrcn discharge device including a/ hanouter pair of Vcoaxial ing vgrid members provided between said axiallyspaced annular discs in apertures in each of the wallsofsaid cylinders,a connecting tube between "and a loop ot wire projecting cathode, a gridsurrounding/said cathode; inner pairof coaxial sheet-metal cylinderssurrounding said grid and joined at their ends yby lanniiva'rdiscs.Sheet'LnietaI/cyIinders joined at theirmends by lannular discs, saidin'iierv and said outer pairs beingcoaxial with each other, a pairl of'axiallyy spacevdynhllflar `discs beteween said t inner and 'o uterfypairs of 'cylinders' interme-` diatethe endsofuthe cylinders providingasubstantially; ficiii-i'mcl .driftgspaceg and generauy i longitudinallyyyextendingI grid, membersjgsubstan'- tially cc'iexten'sivev withIthe'./cattlcde and' 'provided between said axiallyspaced annular discsiny aper, tufee each wie' wins oran, cylinders., f-

